Motor vehicles include an air intake system configured to provide measured quantities of filtered outside air to the internal combustion engine. The outside air is drawn in through an air filtration system, possibly continuing through a throttle body and delivered to the air intake manifold of the engine. The operation of the internal combustion engine with its air intake, fuel combustion and exhaust cycles taken together with the opening/closing operation of the air intake valves presents a problematic source of unwanted noise generation within the air intake tract. This internal combustion engine originated noise may travel in a direction opposing intake air flow back through the air intake tract to radiate from an intake end of the air intake tract or to potentially radiate through the walls of the air intake tract by the sympathetic vibration of the intake tract walls in response to pressure variations (sound pressure variations) within the intake tract.
The engine generated noise in the air intake tract may occur over a wide range of frequencies with the particular sound frequency spectrum depending upon the operating parameters of the engine, such as engine RPMs and engine load, for example. This noise present in the air intake tract within the engine compartment may find its way into the passenger compartment of the vehicle by various paths, for example, through the intervening firewall, through the floor panels or through open vehicle windows. The air intake tract noise, when it reaches the passenger compartment, may be experienced as a nuisance, or even as an indication of poor vehicle design and poor quality.
It is known to treat engine noise in the air intake tract by providing one or more resonator chambers such as, for example, Helmholtz resonators, connected into the air intake tract. While such solutions are known to be beneficial in attenuating intake tract noise, the additional components add expense, intake system complexity and required addition under hood space to install and integrate the components with the air intake system.
It is a known problem that motor vehicle engine compartments must provide space for and integrate a variety of engine associated components including batteries, alternator, air conditioning compressor and heat exchangers, engine coolant systems, transmission, as well as the air intake system and air filtration system for the engine. With the increasing trend towards smaller, lighter, more fuel efficient vehicles and the resulting reduced engine compartment space, the limited packaging space for air intake components and acoustic treatment devices is becoming ever more scarce and valuable. It is also known that providing space under the hood to integrate sound treatment devices may not be a high priority for vehicle designs and engineers, particularly when the need for sound treatment is not identified until late in the vehicle design and build cycle. At a later point in the vehicle design the available packaging space under the hood is what it is and cannot be readily changed to accommodate new components.
Therefore, there remains a need in the art for a compact tuned acoustic attenuation device that requires a minimal of installation space and is easily integrated into the available under hood space. Additionally, there remains a need for a tuned acoustic attenuation device that is operable in a single compact device to provide broadband noise attenuation over a selected range of frequencies.